Current ultra-ultra-large-scale integrated circuits demand increase in component-mounting density, and various microfabrication technologies are now under research and development. The design rule is already in the sub-half micron order. One of the technologies developed for satisfying the severe requirements for miniaturization is chemical mechanical polishing (CMP) technology.
The technology allows, in the production process for semiconductor devices, complete flattening of the light-irradiating layer and thus alleviates the load of light-irradiating technology, and increases the yield of semiconductor devices, and it is a technology essential, for example, in flattening of an interlayer insulation film or a BPSG film, performing shallow trench isolation, and the like.
Fumed silica-based abrasive slurries have been used commonly as CMP abrasives used in flattening an inorganic insulation film layer such as the silicon oxide insulation film formed by plasma CVD (Chemical Vapor Deposition) or low-pressure CVD in the production process for semiconductor devices.
The fumed silica-based abrasive slurries are produced by granulating silica particles, for example by converting silica particles into silicon tetrachloride under heat, and then adjusting the pH of the resulting particles. However, the fumed silica often caused a problem that it adhered to the polishing substrate and the deposited particles could not be removed completely even after washing.
In addition in the conventional CMP methods of flattening interlayer insulation film, the polishing rate is significantly dependent on the pattern of the film to be polished on the substrate; the polishing rate in the raised region varies significantly according to the difference in pattern density or size; polishing of the raised region is inevitably accompanied with polishing of the dent region; and thus, the convention CMP methods had a problem that it could not flatten the insulation film over the entire wafer surface at high level.
In the CMP method of flattening interlayer insulation film, it is necessary to terminate polishing of the interlayer insulation film in the middle, and a process control method of adjusting the polishing depth by polishing period is generally used. However, the method had a problem that the polishing rate varied distinctively not only by the difference in pattern level-difference shape but also by the condition of the polishing cloth and others, which prohibited easy process control.
In the generation of a design rule of 0.3 μm or more, LOCOS (local oxidation of silicon) has been used for separation of elements in integrated circuit. Further increase in processing density since then demanded a technology allowing narrower element separation width, and shallow trench isolation technology is now used more frequently. During shallow trench isolation, CMP is used for removal of the excess silicon oxide film formed on substrate, and a stopper film having a smaller polishing rate is formed beneath the silicon oxide film for termination of polishing. Silicon nitride, for example, is used for the stopper film, and the difference in polishing rate between the silicon oxide film and the stopper film is desirably larger.
On the other hand, cerium oxide abrasives have been used as abrasives for use on the surface of glasses such as photomask and lens. Cerium oxide particles are softer than silica or alumina particles, less likely to cause scratching on the polishing surface, and thus, useful for final mirror-surface polishing. However, such cerium oxide abrasive slurries for glass surface polishing contain dispersants containing sodium salts, and thus, could not be used as abrasives for semiconductor devices. Further, cerium oxide abrasives were more expensive than fumed silica abrasives, and thus, the abrasive was often used at low concentration. For that reason, the cerium oxide abrasive slurries had a problem that the efficiency of polishing the polishing surface was lower in the early polishing phase and the polishing period was elongated undesirably, compared to that by using the fumed silica abrasive.
Accordingly, proposed in Japanese Patent Application Laid-Open No. 2005-159351 was a method of polishing with an abrasive slurry containing fumed silica at higher concentration in the early coarse-polishing step for removal of the level difference on polishing surface and with an abrasive slurry containing cerium oxide particles at low concentration in the subsequent step of polishing until the stopper silicon nitride film.
An object of the present invention is to provide a CMP abrasive slurry for polishing insulation film that allows efficient and high-speed polishing of insulation films such as of SiO2 and SiOC for use in the CMP method of flattening an interlayer insulation film, a BPSG film, an insulation film for shallow trench isolation, and a wiring-insulating film layer, a polishing method by using the abrasive slurry, and a semiconductor electronic part polished by the polishing method.